SODIUM CARBONATE 97
Gay-Lussac degree = i-oi English, degree = 1-71 German degree = 1-58 Des-
17. Complete Analysis.—100 grams of the soda are dissolved in a
beaker in hot water and the liquid allowed to stand in the hot for half an
hour, after which it is filtered through a filter dried at 100° and tared, the
insoluble matter being washed with hot water and used for determination
(a). The filtrate is collected in a litre flask and made up to the mark on
cooling, being used for the determinations (b) to (h).
(a) INSOLUBLE RESIDUE. The insoluble matter, dried at 100°, is
weighed. It is then moistened with water, lixiviated with hot, dilute hydro-
chloric acid (which dissolves the ferric oxide, alumina, calcium and mag-
nesium carbonates), washed with water, redried at 100° and weighed ;
this represents sand and carbon (%). After ignition the sand is weighed
alone and the carbon then obtained by difference.
(b) TOTAL ALKALINITY AND SODIUM CARBONATE. 10 c.c. of the solution
( = i gram of substance), diluted with water, are titrated in the cold with
N-HC1 (methyl orange). This gives total alkalinity, due to carbonate,
hydroxide and sulphide ; deduction from the volume of acid used of those
corresponding to the hydroxide and sulphide (determinations c and d)
and multiplication of the remainder by 53 gives the grams of Na 2C03 per
100 grams of the soda.
(c) SODIUM HYDROXIDE. 100 c.c. of solution (=10 grams of sub-
stance) are shaken in a 200 c.c. flask with excess of barium chloride (10 c.c.
of 10% solution usually suffice), made up to volume, again shaken and
left to stand ; loo c.c. of the clear liquid (not filtered) are pipetted off and
titrated with N-hydro chloric acid in presence of phenolphthalein. This
gives alkalinity due to hydroxide and sulphide together; subtraction of
the corresponding number of c.c. from determination (d) and multiplication
of the remainder by 0-8 gives percentage of NaOH.
(d) SODIUM SULPHIDE. 50 c.c. of solution (=5 grams of substance)
are heated to boiling, treated with ammonia and ammoniacal silver nitrate
solution (13-82 grams Ag per litre) l run in from a burette until no further
black precipitate is produced. To determine the end-point the more readily,
the liquid is filtered towards the end of the titration and the latter con-
tinued in the filtrate. The number of c.c. of silver solution, multiplied
by o-i, gives the percentage of NaaS in the sample. I c.c. of silver solution
— 0-13 c.c. of N-acid (for calculations indicated in b and c).
(e) SODIUM SULPHITE. 50 c.c. of the solution (= 5 grams of substance)
are acidified with acetic acid and titrated with N/io-iodine in presence of
starch paste. The number of c.c. used, multiplied by 0-1261, gives the
percentage of NaoSO;) in the sample.
When sulphides are present, the number of c.c. of iodine solution used
must be diminished by that corresponding with the sulphide found as in
(d), knowing that I c.c. of silver solution = 1-3 c.c. N/io-iodine.
(/) SODIUM CHLORIDE. With ammonia soda, 20 c.c. (=2 grams of
1 13-82 grams of pure silver are dissolved in nitric acid, 250 c.c. of ammonia being
added and the liquid diluted to i litre, i c.c. of this solution = 0-005 gram Na2S.
A.C. 7n aly for delicate colours, should not contain iron. l.2o